1. Field of the Invention
The present invention relates to a wave plate type compressor in which a piston reciprocates in response to the rotation of a wave plate secured to a rotary shaft.
2. Description of the Related Art
In a conventional swash plate type compressor, one head of a double-headed piston completes a single compression cycle for every rotation made by the swash plate and the rotary shaft. On the other hand, with compressors using a wave plate, one head of the double-headed piston completes a plurality of compression cycles in accordance with the shapes of the cam surfaces or cam grooves on the wave plate for each rotation of the rotary shaft. The wave plate type compressors therefore have an advantage over the swash plate type compressor in that the discharge displacement per rotation is increased.
Conventional wave plate type compressors are disclosed in Japanese Unexamined Patent Publication No. 57-110783 and Japanese Unexamined Utility Model Publication No. 63-147571. In the compressor described in the Japanese Unexamined Patent Publication No. 57-110783, in particular, rollers 53 and 54 are provided between an associated double-headed piston 52 and the front and rear cam surfaces 51a and 51b of a wave plate 51 as shown in FIG. 13. The rollers 53 and 54 are rotatably fitted in the piston 52, and are capable of rolling on the wave plate 51. As the wave plate 51 rotates, its cam surfaces 51a and 51b engage and displace the rollers 53 and 54. These rollers then transmit this displacement to the piston 52, in turn, causing its reciprocation.
In the compressor described in the Japanese Unexamined Utility Model Publication No. 63-147571, cam grooves are formed on the front and rear surfaces of the wave plate instead of the cam surfaces. In this publication, balls rather than rollers are interposed between the cam groove and double-headed piston.
Although the rollers or balls may at first appear to be in line contact with the wave plate, a microscopic view reveals a plane contact exists between the contacting components due to their deformation under pressure. This deformation results in the occurrence of the so called "Hertz" contact which effectively increases the contact area shared between the rollers or balls and the wave plate.
To improve the durability of the compressor, it is important to reduce the contact pressure between the above contacting components. This can be done by increasing the length of the line contact or reducing the curvature of the contact portion (i.e., by increasing the radius of curvature). It is apparent, on a microscopic level, that a reduction in the curvature of the contact portion causes an increase in the contact area, and thus reduces the overall contact pressure.
Contact pressure can thus be reduced by increasing the contact area between the wave plate and either the length or diameter of the rollers or the diameter of the balls. Increases made to the length or diameter of the rollers and balls, however, are limited by the diameter of the piston, since each roller or ball is fitted to its associated piston. Such increases tend to increase the size of the piston as well as the compressor. Given the trend toward increasingly compact compressors, increases to the size of the compressor are distinctly disadvantageous.